The accusations by the Local Coordination Committees were issued as Western officials urged opposition forces to regroup because they have no central body with which to work, CNN reported.

If LCC's claim is true, the use of such weaponry means the Syrian regime has introduced a devastating new element into a conflict that has already seen Syrian military drop jury-rigged explosives from helicopters.

Vacuum bombs, formally known as thermobaric explosives, mix fuel with air in the atmosphere to produce a longer-lasting blast that ruptures the lungs, the U.S. Defense Intelligence Agency said in a 2002 study.

In another airstrike, the Syrian military dropped old storage tanks packed with explosives from a helicopter on a line of people waiting for bread at a makeshift bakery in rebel-held town 12 miles west of Aleppo, killing at least 15 people, activists and witnesses said.

The opposition Syrian Network for Human Rights put the number of dead on Thursday at 141, including 48 around Damascus and 53 around Aleppo.

Diplomatic efforts to end the fighting have been stymied, with Russian Foreign Minister Sergey Lavrov complaining Thursday the various factions fighting the Bashar Assad regime have no central body.

U.S. Secretary of State Hillary Clinton earlier called for an overhaul of Syria's exile-led opposition political coalition, saying it has been largely ineffective, in part because it includes aging figures who have not been in Syria for decades.

She said Washington preferred to support those fighting regime forces on the front lines.

A weekend cease-fire sought by United Nations Lakhdar Brahimi was not observed by either side.

Syrian rebels said they were now arming anti-regime Palestinians living in a Damascus enclave to fight pro-regime Palestinians in the same former refugee camp in a move observers said could fuel long-feared violence within Syria's large Palestinian population.

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